Cooling system

ABSTRACT

A cryogenic medical system includes a medical device and a console connectable to the medical device at a connection point. The console controls the temperature of the medical device. The console includes a first cooling system directing coolant to the medical device at a first temperature along a coolant supply line and a second cooling system chilling the coolant within the coolant supply line to a temperature below the first temperature before the coolant reaches the connection point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/638,208, filed Aug. 11, 2000, which is acontinuation-in-part of U.S. patent application Ser. No. 09/489,646,filed Jan. 24, 2000, which claims priority from U.S. Provisional PatentApplication No. 60/117,175, filed on Jan. 25, 1999.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates to a coolant system for a catheter ortreatment wand used for cryotreatment of tissue. In particular, thecoolant system is of the type which connects to a catheter and pumpscoolant through the catheter to chill a region of the catheter, such asthe distal tip, for treating tissue.

BACKGROUND OF THE INVENTION

A number of cooled catheter systems have been developed for treatingtissue in a cardiac setting, either to cool the tissue sufficiently tostun it and allow cold mapping of the heart and/or confirmation ofcatheter position with respect to localized tissue lesions, or to applya more severe level of cold to ablate tissue at the site of the catheterending. In general, the range of treatments which may be effected by acryocatheter is comparable to the range of applications for radiofrequency or thermal ablation catheters, and in particular, theseinstruments may be configured to achieve either small localized ballshape lesions at the tip of the catheter, or one or more elongatedlinear lesions extending a length of several centimeters or more alongthe tip. The latter form of lesion is commonly used to achieveconduction block across a region of the cardiac wall so as to sever anaberrant pathway over a length, preventing conduction across the region,in order change the cardiac signal path topology, for example, toeliminate a faulty pathway responsible for atrial fibrillation or atachycardia.

In general, when used for endovascular access to treat the cardiac wall,catheters of this type, in common with the correspondingearlier-developed radio frequency or electrothermal ablation catheter,must meet fairly demanding limitations regarding their size,flexibility, and the factors of strength, electrical conductivity andthe like which affect their safety and may give rise to failure modes inuse. These constraints generally require that the catheter be no largerthan several millimeters in diameter so as to pass through the vascularsystem of the patient to the heart. Thus, any electrodes (in the case ofmapping or RF/electrothermal ablation catheters), and any coolantpassages (in the case of cryocatheters) must fit within a catheter bodyof small size.

A number of different fluids have been used for the coolant component ofprior art cryotreatment catheters, such as a concentrated salinesolution or other liquid of suitably low freezing point and viscosity,and of suitably high thermal conductivity and heat capacity, or aliquified gas such as liquid nitrogen. In all such constructions, thecoolant must circulate through the catheter, thus necessitating multiplepassages leading to the cooling area of the tip from the catheterhandle.

Furthermore, conditions of patient safety must be considered, raisingnumerous problems or design constraints for each particular system. Thusfor example, a high pressure may be required to circulate sufficientcoolant through the catheter body to its tip and back, and the overalldesign of a catheter must be such that fracture of the catheter wall orleakage of the coolant either does not occur, or if it occurs, isharmless. Further, for an endovascular catheter construction, thepresence of the coolant and circulation system should not substantiallyimpair the flexibility or maneuverability of the catheter tip and body.

To some extent these considerations have been addressed by using a phasechange material as the cryogenic fluid, and arranging the catheter suchthat the phase change, e.g., from a liquid to a gas, occurs in thetreatment portion of the catheter tip. Another possible approach is toemploy a pressurized gas, and configure the catheter for cooling byexpansion of the gas in the tip structure. However, owing to the smallsize that such a catheter is required to assume for vascular insertion,or the awkwardness of handling a cryogenic treatment probe generally,the design of a safe and effective coolant circulation system whichnonetheless dependably provides sufficient cooling capacity at a remotetip remains a difficult goal.

Among other common problems to be addressed while providing adequatethermal capacity, may be noted the leakage problem mentioned above, theproblem of effectively preventing the catheter as a whole from beingexcessively cold or damaging tissue away from the intended site, and theproblem of conduit or valve blockage owing for example to ice particlesand the like.

Accordingly, it would be desirable to provide a coolant system whichconveniently attaches to a cryocatheter.

It would also be desirable to provide a coolant system which injects andretrieves the coolant from the catheter to allow continuous operationwithout leakage into the environment or other loss of coolant.

It would further be desirable to provide a treatment system whichprecisely controls ablation and treatment regimens by conditioning thecoolant supply at various point along the fluid path.

SUMMARY OF THE INVENTION

These and other desirable features are obtained in a coolant system thatincludes a medical device and a console connectable to the medicaldevice at a connection point. The console controls the temperature ofthe medical device. The console includes a first cooling systemdirecting coolant to the medical device at a first temperature along acoolant supply line and a second cooling system chilling the coolantwithin the coolant supply line to a temperature below the firsttemperature before the coolant reaches the connection point.

BRIEF DESCRIPTION OF DRAWINGS

These and other features of the invention will be understood byreference to the description below, read in light of the prior arttogether with illustrative figures, wherein:

FIGS. 1 and 1A illustrate a cryocatheter treatment system andcryocatheter;

FIG. 2 is a schematic representation of a coolant system in accordancewith one embodiment of the present invention for use with the catheterof FIG. 1;

FIG. 3 is a detailed schematic of another implementation of the coolantsystem of the present invention;

FIG. 4A is a schematic illustration of still another coolant systemconfiguration;

FIG. 4B is an enthalpy graph with respect to the system of FIG. 4A;

FIG. 5A is a schematic illustration of yet another coolant systemConfiguration;

FIG. 5B is an enthalpy graph with respect to the system of FIG. 5A;

FIG. 5C is another enthalpy graph with respect to the system of FIG. 5A;

FIG. 6 schematically represents a refrigerant subcooler that can beincluded in the coolant system configurations of the invention;

FIG. 7A illustrates another configuration for a subcooler;

FIG. 7B is an enthalpy graph with respect to the system of FIG. 7A;

FIG. 7C is a schematic illustration of yet another coolant systemconfiguration;

FIG. 7D is a schematic illustration of yet another coolantconfiguration;

FIG. 8A illustrates still another configuration for a subcooler;

FIG. 8B illustrates still another configuration for a subcooler;

FIG. 9 is a schematic illustration of still another coolant systemconfiguration; and

FIG. 10 is a schematic illustration of still another coolant systemconfiguration.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a cryogenic treatment system 100 illustrating the generalelements thereof. System 100 includes a treatment catheter 110 having ahandle 110 a, a treatment console 120 and number of connecting lines 115which include signal lines for any monitoring or mapping functions aswell as a coolant injection line 115 a and a coolant return line 115 b.As illustrated, the console includes a display screen 120 a which may,for example, show both cardiac electrical signals and various status andcontrol screens related to setting or reporting the cooling functions ofthe catheter or the ablation regimens being administered therewith.

FIG. 1A shows in slightly greater detail a catheter 110 used in a systemin accordance with the present invention. As shown, the handle 110 a isequipped with input ports for an electrical connector 111, a coolantinjection tube connector 112, and a return tube connector 113. Theseconnect via various internal junctions or tubes passing through thehandle to provide these three functions to the distal tip of thecatheter. The handle may also include various control assemblies, e.g.,switches or valves, as well as safety detection or shut down elements(not illustrated).

Leading from the handle 110 a is an elongated catheter body 110 b whichextends to the catheter tip 110 c, illustrated in enlarged detail toshow a representative structure thereof. As shown, in catheter tip 110 cthe coolant enters through a central tube 1 and exits via a nozzle 2 atthe end of the tube to expand in a small contained region forming achamber 3 at the tip of the catheter. In the illustrated construction,the tube 1 runs concentrically within an outer tube (not numbered)thereby forming an annular return space 4 surrounding the supply tube 1and extending back to the fluid return connector 113 of the handle. Asdiscussed further below, the return passage for expended coolant is avacuum passage, thus assuring that leakage into the blood stream cannotoccur.

The location of chamber 3 defines the cooling region of the cathetertip. In the illustrated embodiment this is a short chamber less than acentimeter long located at the very tip of the catheter. Also shown area thermocouple 5 positioned within the tip to sense tip temperature, anda plurality of electrodes including a tip electrode 7 a and one or morering electrodes 8 a, 8 b . . . which are positioned near the tip for usein mapping and/or detecting cardiac signals. In other embodiments, thechamber 3 defined at the tip of the catheter may be an elongated chamberseveral centimeters in length for defining a coolant chamber effectiveto form linear lesions when placed in contact with tissue such as thecardiac wall. For the linear embodiment, multiple expansion nozzles, aperforated inlet tube end segment, or other variation in theconstruction of the coolant supply line may be used to assure a highrate of cooling along the full length of the expansion chamber.Furthermore, the chamber wall may be very thin, or formed with a metalsleeve or cap to achieve high heat transfer rates. Other structureswithin the catheter may include torque or steering wires, or otherelements conventional in the art for navigation of the catheter pastbranch points in vessels, and for urging the catheter tip into contactwith a wall once its position is confirmed.

As will be understood from the above, the task of the console is toprovide coolant at the tip region in sufficient quantity and for timeseffective to create the desired lesions. The nature and depth of thelesions created will depend on a number of factors, including thetemperature attained in the adjacent tissue, as well as the nature ofthe cooling cycle by which that temperature is attained. In general whenthe tissue attains an extremely low temperature, or a temperatureeffective to create ice crystals within tissue cells, the tissue damagewill be irreversible, resulting in effective ablation at the contactedsite. The actual cooling rates achieved at the tip will depend to alarge extent on the area of contact with the tissue as well as theconductive properties of the adjacent tissue and the structure andgeometry of the catheter in addition to the nature of coolant flowpassing through the catheter tip. In the present system the latterquantity is controlled, as discussed more fully below, by providing acontroller in which the flow of a phase change coolant supplied to thetip is varied to directly control the amount of cooling power availableduring an ablation cycle. In addition, the primary cooling effect isachieved by expansion of coolant at the inlet nozzle 2 as it enterschamber 3.

While not illustrated, one or more electrical sensing elements inaddition to the thermocouple may be provided at various places withinthe catheter to provide useful feedback or emergency control functions.For purposes of the present patent application, such functions will notbe further discussed. However, if provided they may be positioned in adiscrete cooling system, which for purposes of illustration may beconsidered to lie entirely within the console 120, or be externalthereto, but in any case to function in relation to the coolant supplyelements which will now be described below.

FIG. 2 illustrates one embodiment of a cooling system in accordance withthe present invention configured to connect to the inlet and returnports 112, 113 of the catheter 110 (FIG. 1A). As shown, the coolantsystem 120 includes a coolant supply 30, a coolant conditioner 40, acoolant control 50 and a coolant return section 60. The control section50 connects to the inlet 112 of the injection catheter, for example by asupply tube, while the return system 60 connects to coolant return port113. These are illustrated as separate connections, but as discussedmore fully below, they may be implemented with a single vacuum-jacketedline with a quick connect coupler, or other specialized connection whichallows a single coupling to the catheter handle for all coolantfunctions. Similarly, electrical connections may be incorporated in sucha single conduit, or may be provided as separate signal cabling.Operation of the coolant system 120 will be most fully understood from adetailed discussion of each of the subassemblies 30, 40, 50, 60.

In general terms, the coolant system has a coolant conditioning section40 with a compressor that provides a conditioned phase change coolant atelevated pressure to the control section 50, which, in turn, regulatesthe supply of coolant provided to the inlet of the catheter. The returnsection 60 includes a vacuum pump which continuously draws expendedcoolant from the catheter at lower pressure and returns it at higherpressure to the coolant conditioner 40, thereby providing a closedcirculation loop through the catheter to meet the required ablation ormapping regimens. In the preferred embodiment, the conditioner providescoolant substantially at ambient temperature or colder, and thecontroller includes an electronically controlled pressure regulatorwhich sets the flow rate of the coolant injected into the catheter, thusregulating the cooling action of the catheter tip. Conditioned coolantis provided to the control section by the conditioner 40, which receivescoolant at lower pressure either from the return section 60 or from thesupply 30, compresses the coolant to a high pressure, liquefies thecoolant, and brings it to approximately ambient temperature at itsoutlet line 42 a leading to the controller. As further shown in FIG. 2,the output from the compressor has a second branch 42 b in which excesscoolant is not further cooled, but is simply returned to the supply 30.

As noted above, conditioner section 40 in addition to the raising thepressure of the coolant supplied to the regulator for controlledinjection into the catheter, also conditions the temperature of the highpressure coolant. This is preferably done as shown in FIG. 2, by heatexchange between the inlet supply line 41 and the compressor outlet line42. As shown in the figure, the compressor outlet line 42 is placed inheat exchange communication, for example via a condenser or heatexchanger 45 b, with the inlet line 41. In addition one output branch 42a of the outlet line 42 is placed in heat exchange communication, forexample via exchanger 45 a, with an upstream portion of the inlet line41. The compressor 43 operates to compress the coolant from a relativelylow pressure, preferably below atmospheric, to a considerably higherpressure, e.g., 20 to 30 atmospheres as measured in its outlet line 42.The material in line 42 is therefore heated by compression, and the heatexchange with inlet line 41 serves to reduce the temperature risegenerated by compression. Furthermore, by providing only a portion ofcompressor output, namely the catheter-directed branch 42 a to theupstream, colder portion of the compressor inlet line 41, the catheterinjection supply of coolant is effectively brought to or near ambienttemperature or colder, while the downstream heat exchange effected inheat exchanger 45 b with the entire output of the compressor is cooledto a lesser extent, serving a more traditional function of liquefyingthe coolant output and enhancing the overall cooling capacity of thecompressed fluid. This ordered heat exchange arrangement providespreferentially greater cooling to the catheter-directed supply line,resulting in a stabilized catheter input over a broader range ofoperating cycles.

In FIG. 2 the high pressure return 42 b to the tank may be implementedwith a pressure regulator located in-line ahead of the tank inlet toassure that coolant is returned to the tank only when its use elsewherein the circulation loop is not required, and that the pressure in theline first builds up to a level higher than the current tank pressure.

Thus, the system of the present invention provides a closed-loop coolantcirculation system wherein coolant is conditioned for provision to theinlet of a control module which injects the coolant into a catheter, andthe coolant returns in a closed-loop to provide a continuous circulationof fluid at ambient temperature or colder into the catheter.

FIG. 3 shows a prototype embodiment in greater detail, illustratingrepresentative valves and regulators for implementing a preferredclosed-loop coolant supply 200. The coolant supply, compressor, controland return portions of system 200 are numbered with numerals 230, 240,250, and 260 corresponding to the related subassemblies 30, 40, 50 and60 of system 20. As shown in this embodiment, a refrigerant tank 231equipped with a magnetic sight glass 231 a to indicate fill level,supplies refrigerant through a needle valve 232 along line 233 to adownstream pressure regulator 235. The pressure regulator 235 convertsthe nominal tank pressure of several hundred pounds per square inch to afixed level of 14 psia to provide a constant supply pressure to theinlet line 241 of the compressor. At this stage the refrigerant isboiling at a temperature of about −60° Fahrenheit. The vacuum recoveryreturn line 262 joins the refrigerant inlet 241 at this point.

The compressor inlet line 241 passes through heat exchanger 245 en routeto the compressor 243, and also passes through a condenser 244, so thelow pressure liquid in the inlet line 241 is heated by the hot vaporcoming out of the compressor, causing it to become a vapor. Thecompressor 243 takes the vapor and pressurizes it to about 400 psi. Thepressurized output passes along line 242 through dryers D and sightglass SG, after which the high pressure outlet line bifurcates into twobranches 242 b and 242 a. An upstream pressure regulator 246 in line 242b builds and maintains pressure in the high pressure output lineallowing the regulator to open and return excess refrigerant to the tank231 when the pressure reaches a preset level, of about 400 psi, which ishigher than the nominal tank pressure, e.g., 200 psi.

The second branch 242 a of the output line 242 passes through the heatexchanger 245 located in the upstream portion of the input line 241,where it is further cooled to provide a conditioned output to thecontroller 250, which as shown includes a motorized pressure regulator254. Pressure regulator 254 controls the flow rate of coolant providedalong line 251 to the inlet port of the catheter (illustratedschematically). By way of example, the pressure regulator 254 may becontrolled by a control microprocessor in the console to provide coolantat a pressure of 250 psi for a time interval of 2.5 minutes. Control isgenerally done by actuating the motor of regulator 254 to achieve adesired set point and leaving the regulator at that setting for theindicated time period. A zero to 500 psi pressure transducer 255 isplaced in line 251 to provide feedback signals for implementing thecontrol of the regulator 254, which may further employ feedback from thethermocouple in the catheter.

The foregoing values of pressure and duration are given by way ofexample only, and it will be understood that typical cooling regimensimplemented by the control console 120 (FIG. 1) may run from severalseconds to five minutes or more, and that the coolant pressures whichare varied to achieve a desired rate of heat transfer or effectivelesion depth may vary from the coolant pressure in the tank toapproximately the pressure of the compressor output line 242 a.Advantageously, the pressure in line 251 remains greater than thesaturation pressure of the refrigerant being used such that it does notstart to boil before it reaches the tip.

As further shown in FIG. 3, the return line 115 b from the catheterattaches to vacuum section 260, while a solenoid operated purge valve257 extends between the catheter inlet line 251 and the low pressurereturn line 262 from the vacuum scavenging system 260. It will beunderstood that purge valve 257 will typically be operated to bleed theinlet line when the catheter is first attached and the supply compressoror return pump, respectively, are operated.

The return line 115 b from the catheter passes via vacuum protectionsolenoid-operated valve 261 to a vacuum pump 265, which maintains avacuum in the range of 2 to 40 millibars in the return line, and whichincreases the pressure of the expended coolant vapor to approximately 15psi. At the outlet side of the vacuum pump a similar solenoid operatedprotection valve 261 a is provided together with a check ball, and anoil filter OF which prevents pump oil from contaminating the circulatingcoolant or depositing in the coolant valves, catheter passages or othercomponents. A filter, e.g., 0.5 μm, appears in the catheter inlet line251. The entire vacuum system may be isolated by the solenoid operatedprotection valves 261, 261 a, during start-up or during a sensedover-pressure or blood leakage condition, and a check valve 265 preventsany pressure build-up on the vacuum pressure side of the catheter in theevent of pump or compressor failure, allowing coolant return directlyinto the return line 262 and compressor inlet 241; For this purpose, thecompressor output or various bypass or check valves 257, 264 are set apressure slightly higher than the output setting of the tank conditionerregulator 235, so that the coolant normally circulates into the catheterand through the vacuum system back into the compressor as a closed-loop.

In the illustrated embodiment, a coolant refill port 275 is provided ata solenoid operated valve 277 in the compressor inlet line 241, allowinga refrigerant bottle attached at that point to employ the samecompressor 243 of the system to refill the supply tank 231. For thispurpose, a solenoid operated by-pass valve 237 is also supplied tobypass the upstream high pressure return regulator 246 between thecompressor output line 242 b and the tank, and speed up refill of thetank 231. Preferably, above the tank, a solenoid operated valve 238connects to a vent port to allow venting of any air which may haveaccumulated in the refrigerant tank due to leakage through the catheteror tubing. This vent is preferably controlled automatically by asuitable control program in the console 120. Venting may be implemented,for example, by providing a temperature sensor in the refrigerant tankand a pressure sensor at its top. Knowing the temperature of the liquidrefrigerant in the tank, the vent may be operated until the saturatedpressure is reached for the given refrigerant at the indicated tanktemperature. Such a venting step is to be performed each time theconsole is turned on. In addition to the foregoing elements, variouspressure indicators or temperature sensors may be situated along thedifferent lines to indicate operating parameters of the fluid therein.These are preferably sensors or indicators of the process control typewherein, rather than a dial display output, they provide an electricaloutput which connects to a microprocessor programmed to monitor thevarious conditions continuously to detect relevant safety, control ormaintenance conditions.

Referring now to FIG. 4A another embodiment of a closed-loop system isshown schematically, wherein letters A through F correspond to points ona system enthalpy graph depicted at FIG. 4B. Of particular interest inthe graph of FIG. 4B are the areas representing a refrigerant in liquidstate, gas state, and a mixed state that includes variable percentagesof liquid and gas.

The system of FIG. 4A includes a compressor 300 that pressurizesrefrigerant in a gas state and passes it through a first cooler orcondenser 302. In the condenser 302, the refrigerant transitions from agas state to a transition or combination liquid and gas state, whereinalmost all of the refrigerant is liquid, or if liquid, very close to thepoint where the refrigerant changes state to a gas. The refrigerantpasses through a filter or contaminant remover 304 and thence to asecondary cooler, referred to herein as a subcooler 306. The subcooler306 chills the refrigerant to a lower temperature than that achieved bythe compressor to cause the refrigerant to be completely in the liquidstate prior to transfer to a catheter 310. In an exemplary system, thesubcooler 306 chills the refrigerant to a temperature colder than 10° C.to enable the catheter tip to be chilled to temperatures as low as −90°C.

Ensuring that the refrigerant is in a liquid state before itsintroduction into the catheter provides significant performanceadvantages over known systems. For example, in order to achieved maximumcooling power and maintain a predictable and controlled tip temperaturefor a coolant injection system as described hereinabove, the refrigerantor coolant should exit the injection tube 1 (see FIG. 1A) as a liquid.However, without a subcooler, the coolant is at or near point “C” asshown in FIG. 4B (at the liquid/gas border). Thus, as it enters thecatheter and begins to warm, bubbles form in the coolant and the coolantexits the injection tube 1 in spurts instead of as a stream. In someinstances, without a subcooler, only 40% or so of the coolant exits theinjection tube 1 as a liquid, as about 60% or so of the coolant hasalready changed state to a gas. Because, there is less fluid to changestate to gas, the cooling power of the device is reduced. Further, theliquid/gas spurts cause significant temperature fluctuations that canadversely affect a selected cryotreatment. Both the reduced coolingpower and the temperature fluctuation phenomena are increasinglypronounced and problematic the more the diameter of the catheter andinjection tube are reduced.

As shown, the subcooler 306 is located within the console 120 or one ofits accessories 115 c. This helps to minimize weight and cost of adisposable handle and or catheter components, and it allows the catheterto be much smaller in diameter than a catheter having a secondary orsubcooler in the handle or in the catheter. Additionally, locating thesubcooler 306 in the console and/or its accessories minimizes the spaceoccupied or required by cooling equipment within the catheter, therebyfacilitating use of very small diameter catheters (e.g., 3Fr to 7Fr) forcryotreatments.

Continuing to refer to FIGS. 4A and 4B, as the refrigerant is ejectedfrom the line leading from the subcooler 306, it is allowed to changephase from a liquid to a gas and to expand in a low pressure or nearvacuum environment created by a vacuum pump 312 at the catheter tip 314.FIG. 4B illustrates the sudden transition from liquid to gas asrepresented by points “D” to “E” to “F” and to “A” on the enthalpygraph. The vacuum pump 312 causes the expanded gas to be returned to thecompressor 300 so the cycle can be repeated.

FIGS. 5A and 5B illustrate another cooling system configuration that issimilar to the closed-loop system shown in FIG. 4A. In this embodiment,there is no compressor 300 or condenser 304. Refrigerant is supplied tothe system from a tank or cartridge 316 in substantially liquid state orvery close to the point where the refrigerant changes state from liquidto gas (point “C” on the graph of FIG. 5B). The refrigerant passesthrough a filter or contaminant remover 318 and then to a subcooler 320.The subcooler 320 chills the refrigerant to a temperature that causesthe refrigerant to be completely in the liquid state (point “D” on thegraph of FIG. 5B) prior to transfer to a catheter 322.

As the refrigerant is ejected from the line leading from the subcooler320, it changes phase from a liquid to a gas and expands at the cathetertip 322 in a low pressure or near vacuum environment created by a vacuumpump 324. FIG. 5B illustrates the sudden transition from liquid to gasas represented by points “D” to “E” to “F” and to “G” on the enthalpygraph. The vacuum pump causes the expanded gas to conveyed to acollection tank or other scavenging system 326. Cryotreatment cancontinue until the refrigerant supply bottle 316 is no longer capable ofproviding liquid refrigerant. Down-time, however, can be minimized if aquick-connect/disconnect mechanism 328 is associated with the supplybottle 316. In an alternate configuration, a vacuum pump is not used andthe expanded gas is directly conveyed to the collection tank or otherscavenging system 326. In still another alternate configuration, theexpanded gas is released to the atmosphere surrounding the system, withno scavenging or collecting system used. Various other configurationswill be apparent to those skilled in the art based on the disclosures ofthe present invention.

Referring now to FIGS. 5A and 5C, an alternate arrangement of a coolingsystem configuration is illustrated. Here refrigerant is supplied to thesystem from the tank or cartridge 316 in a substantially gas state(point “B” on the graph of FIG. 5C). The refrigerant passes through thefilter or contaminant remover 318 (optional) and then to the subcooler320. The subcooler 320 chills the refrigerant to a temperature thatcauses the refrigerant to transition to the liquid state (point “D” onthe graph of FIG. 5C) prior to transfer to the catheter 322.

As the refrigerant is ejected from the line leading from the subcooler320, it changes phase from a first liquid state to a second liquid statepoints “D” to “E”) then to a gas and expands at the catheter tip 322 ina low pressure or near vacuum environment created by a vacuum pump 324.FIG. 5C illustrates the sudden transition from the second liquid stateto the gas state as represented by points “E” to “F” and to “G” on theenthalpy graph. The vacuum pump causes the expanded gas to be conveyedto a collection tank or other scavenging system 326. Cryotreatment cancontinue until the refrigerant supply bottle 316 is no longer capable ofproviding liquid refrigerant. Again, down-time can be minimized if aquick-connect/disconnect mechanism 328 is associated with the supplybottle 316. It is contemplated that the phase states represented by FIG.5C can be employed in any of the structural embodiments constructed inaccordance with the present invention.

Supplying the refrigerant to the chamber 360 in a gas state has theadded advantage of providing consistent control of the flow andtemperature characteristics of the refrigerant. Refrigerant in the gasphase is less susceptible to fluctuations that can occur due to therefrigerant's inherently unstable nature at the gas-liquid transitionphase.

Although a subcooler is shown with respect to the systems of FIGS. 4Aand 5A, such a device can also be included in the systems depicted inFIGS. 2 and 3. A subcooler or subcooling system compatible with thesesystems can include a Peltier cooler, a Joule-Thompson, a Stirlingengine or an independent closed-loop refrigeration system. Additionally,although control of the ratio of gas and liquid in a coolant can beperformed with temperature control, the invention also contemplates useof pressure control in the console and subcooler to control the ratio.

FIG. 6 discloses an exemplary, independent, closed-loop subcooler inschematic form. As shown, the subcooler includes a chamber 330 throughwhich passes a coiled refrigerant transfer line 332. A compressor 334and condenser 336 provide liquid refrigerant that is transferred intothe chamber 330 as shown by the arrow marked “Ref. in.” The coolant, ifcompressed gas expands, or if liquid changes state to gas, therebychilling the transfer line 332 and its contents. The expanded, gas-statecoolant is exhausted from the chamber 330 as shown by the arrow marked“Ref. out” and returned to the compressor 334. A capillary tube 338 canbe interposed between the condenser 336 and the chamber 330 in order toreduce the flow injected in the heat exchanger 330.

Although the subcooler system of FIG. 6, can provide effective coolingperformance, it can also be bulky, noisy, and heat emitting whencompared to the subcooling system of FIG. 7. Referring now to FIG. 7A,an insulated enclosure 340 (like chamber 330) encloses a coiled portionof a coolant supply line 342 leading to a medical implement (not shown)as described above. The coolant supply line 342 is in communication witha coolant reservoir 348 (such as bottled, liquid N₂O) to allow coolantto be directed into the enclosure 340. An outlet 350 in communicationwith a vacuum source 351 is provided to exhaust coolant from theenclosure 340 whereupon it is directed to a scavenging system. Coolingperformance can be controlled with a coolant flow regulator 352 that canbe made responsive to a temperature sensor 354 within the enclosure 340that outputs a signal to a temperature controller 355 that controls theflow regulator 352. As discussed above coolant or refrigerant can besupplied in a liquid phase or a gas phase, for example, FIG. 7B is anenthalpy graph (representing refrigerant supplied in the liquid phase)for the system illustrated in FIG. 7A. Alternately, the enthalpy graphshown in FIG. 5C represents the phases of the coolant along the flowpath (representing refrigerant supplied in the gas phase).

Referring now to FIG. 7C which is a schematic illustration of analternate embodiment of a subcooler. Chamber 360 is depicted having anoutlet 364. Provided within the camber 360 is a conduit 366, having afirst end 367 and a second end 369, defining a fluid flow path for acoolant or a refrigerant. The conduit 366 defines an inlet 362. Inpractice, a refrigerant is supplied to the first end 367 which thenpasses through the body of the conduit 366 to the second end 369. Afterthe refrigerant enters the conduit 366 a portion of the refrigerant isdirected into the chamber 360 via the inlet 362, the refrigerant thenexpands to thereby cool the chamber 360 and in turn the conduit 366. Theexpanded refrigerant is then evacuated from the chamber 360 via theoutlet 364. The rate of flow through the inlet 362 can be controlled bythe size of the inlet 362 as well as by flow control valves as discussedherein (not shown). The diameter of the inlet 362 can range from 0.0001to −0.03 inches. In an exemplary embodiment the diameter of the inlet362 is 0.002 inches. The rate of subcooling affected within the chamber360 can be regulated by adjusting the flow rate of the outlet 364. Bydecreasing the flow rate allowed at the outlet 364, the amount ofrefrigerant entering the chamber 360 via the inlet 362 is therebydecreased and the subcooling reduced. Further, it is contemplated thatthe location of the inlet 362 along the conduit 366 can be varied, forexample, the inlet 362 can be provided closer to the second end 369 thanis shown in FIG. 7C. It is also contemplated the that the location ofthe outlet 364 along the chamber 360 can be varied, for example theoutlet 364 can be provided closer to the first end 367 than is shown inFIG. 7C. In an alternate configuration where a refrigerant is suppliedto the subcooler in a liquid phase, it is advantageous to place theinlet 362 close to the first end 367 and the outlet 364 close to thesecond end 369. Alternatively, when the refrigerant is supplied to thesubcooler in a gas phase, it is advantageous to provide the inlet 362close to the second end 369 and the outlet 364 close to the first end367. It is contemplated that the subcooler shown in FIG. 7C can be usedin systems as shown in FIGS. 4A, 5A, 7A, 9 and 10 as well as other suchsystems.

Referring now to FIG. 7D which is a schematic view of another alternateembodiment of a subcooler illustrated in more detail. FIG. 7Dillustrates another cooling system configuration that is similar to theclosed-loop system shown in FIG. 5A with an alternate subcooler locationand further incorporating the exemplary subcooler arrangement of FIG.7C. Refrigerant is supplied to the system from a tank or cartridge 516in substantially liquid state or substantially gas state as discussed indetail above. The refrigerant passes through a filter or contaminantremover 518 (optional) and then to a junction 519. One branch of thejunction passes through a vent system 521 and the other branch passesthrough subcooler 520. The subcooler 520 chills the refrigerant to atemperature that causes the refrigerant to be in the liquid state priorto transfer to a catheter 522. The arrangement shown in FIG. 7D has theadded advantage of permitting placement of the subcooler withinaccessories external to the console, for example, in an connection boxas shown in FIG. 10 below, in a catheter handle assembly or any othersuch device located between the catheter and the console.

The function of the system shown in FIG. 7D follows that describedabove. It is contemplated that the subcooler embodiment shown in FIG. 7Ccan be used in any of the alternate systems discussed herein. It isfurther contemplated that the physical arrangement of the individualcomponents can follow the layout shown in FIG. 7D as well as otherarrangements disclosed herein.

Referring now to FIG. 8A, yet another configuration for a subcooler isillustrated in conjunction with a control system for the subcooler. Aswith configurations described above, this illustration depicts a chamber360, having an inlet 362 and an outlet 364, provides a flow path forrefrigerant such as nitrous oxide or another fluid. A conduit 366 thatdefines a second fluid flow path for the same refrigerant passes throughthe chamber 360 and is in fluid communication with a refrigerant supplyupstream of the chamber and a medical device downstream from thechamber. As shown, a fluid flow splitter 368 can allow a commonrefrigerant source to be used for supplying the chamber 360 and theconduit 366.

A programmable controller 370 is in communication with and controls oneor more valves, such as a first valve 372, to regulate flow of coolantthrough the conduit 366 and into the medical device in response to aprogrammed cooling profile and in response to sensor outputs from thecatheter. Additionally, the controller 370 can be used to control asecond valve 374 to regulate flow of coolant through the chamber 360 inresponse to sensed temperature within the chamber. For example, thecontroller 370 can establish a duty cycle that opens and closes thesecond valve 374 repeatedly over time. If the temperature rises in thechamber 360 the second valve 374 can be opened and closed morefrequently. By contrast, if the temperature in the chamber falls toofar, the second valve 374 can be cycled less frequently. Another exampleincludes establishing a duty cycle to specifically regulate thetemperature increases and decreases at the treatment site. It has beenfound advantageous to be able to precisely control the freezing andthawing rates when performing a procedure as described above. Further,by sensing the actual temperatures and adjusting the opening and closingof the system valves, the application of specific temperature regimenscan be accomplished.

Referring now to FIG. 8B, yet another configuration for a subcooler isillustrated in conjunction with a control system for the subcooler. Thesubcooler feature is provided by a thermoelectric cooler 400, such as apeltier cooler, the operation of which is known in the art. Thethermoelectric cooler has a hot side 420 and a cold side 440. A conduit466 is provided adjacent and in thermally-conductive communication withthe cold side 440 of the thermoelectric cooler 400. A supplementalcooler 460 is provided adjacent to and in thermally-conductivecommunication with the hot side 420 of the thermoelectric cooler 400.The conduit 466, the thermoelectric cooler 400 and the supplementalcooler 460 are enclosed by a housing 480. The supplemental cooler 460 isconnected to an external cooling source 500 which can be any of thecooling arrangements disclosed herein or other such devices, forexample, a compressor system as shown in FIG. 6 can be used.

Operation of the device shown in FIG. 8B is now discussed. When thethermoelectric cooler is activated, the temperature of the cold side 440is reduced and thereby reduces the temperature of the adjacent conduit466, which in turn reduces the temperature of refrigerant passingthrough the conduit 466. Further, the hot side 420 increases intemperature. The cooling source 500 supplies cold energy to thesupplemental cooler 460 which thereby cools the adjacent hot side 420.By cooling the hot side 420, heat is removed from the housing 480 andthe cooling efficiency of the supplemental cooler 460 is increased. Asdescribed above, it is desirable to provide a reduced temperature to theconduit 466 to thereby liquify any refrigerant or coolant that is passedthrough the conduit 466. It is further contemplated that the hot side420 can be cooled by more conventional means such as moving air acrossthe hot side 420. Additionally, a heat sink can be provided in thermalcommunication with the hot side 420 to increase cooling efficiency.Operations of such devices will be readily apparent to one skilled inthe art based upon the disclosure of the present invention.

As discussed above, one significant advantage provided by the presentinvention is that subcooling systems can be located within the console120 or its accessories 115 c instead of in the catheter or in thecatheter handle (the part held by the surgeon to manipulate thecatheter). Thus, as used by applicant, “console” is intended to mean anycomponent that is not a part of the operative implement. For example, inthe systems shown, the “console.” can be considered to be everything butthe catheter and the handle. Illustrations of this feature are shown inFIGS. 9 and 10, wherein FIG. 9 illustrates exemplary subcooling systemcomponents 380 being located entirely within the console 120. FIG. 10illustrates a system wherein a subcooler 382 is positioned within an ECGconnection box 384. Although the subcooler 382 can be configured forcooling as described above, it can include any other known coolingdevice that can be located within an accessory such as an ECG connectionbox.

The invention being thus disclosed and described in illustrativeembodiments herein, variations and modifications as well as adaptationsof the invention to other systems will occur to those skilled in theart, and all such variations, modifications and adaptations areconsidered to lie within the scope of the invention as described hereinand defined in the claims appended hereto and equivalents thereof.

1-46. (canceled)
 47. A method of cooling a medical device, comprisingthe steps of: obtaining a first refrigerant in a gaseous phase from acoolant source; providing the first refrigerant under pressure to afirst cooling system; obtaining a second refrigerant in a liquid phasefrom the coolant source; sub-cooling the first refrigerant to atemperature below a critical temperature thereof using the secondrefrigerant to liquefy the first refrigerant; expanding the sub-cooledfirst refrigerant in proximity to the medical device; and removing theexpanded first refrigerant from the proximity of the medical device. 48.The method according to claim 47, wherein the coolant source is apressurized tank containing refrigerant therein.
 49. The methodaccording to claim 47, wherein the step of providing the firstrefrigerant under pressure includes pressurizing the coolant with acompressor.
 50. The method according to claim 47, wherein the step ofsub-cooling the first refrigerant includes expanding the secondrefrigerant in a second cooling system, and placing the second coolingsystem in a heat-exchange relationship with the first cooling system.51. The method according to claim 47, wherein the steps of obtaining afirst refrigerant and obtaining a second refrigerant from the coolantsource include routing the first and second refrigerants through a fluidflow splitter.
 52. The method according to claim 47, wherein the firstrefrigerant is sub-cooled to a temperature of less than approximately 10degrees Celsius.
 53. The method according to claim 47, wherein the firstrefrigerant is NO2 in gaseous phase, and the second refrigerant is NO2in liquid phase.
 54. The method according to claim 47, furthercomprising the step of recovering the expanded first refrigerant into ascavenging system.
 55. An cryogenic medical system, comprising: acoolant source providing a first refrigerant in gaseous phase, and asecond refrigerant in liquid phase; a first cooling system receiving thefirst refrigerant from the coolant source; a second cooling systemreceiving the second refrigerant from the coolant source, wherein thesecond refrigerant is expanded in the second cooling system, and whereinthe second cooling system is in a heat-exchange relationship with thefirst cooling system such that at least a portion of the first coolingsystem is sub-cooled by the second cooling system; and a catheterdefining an expansion chamber therein, wherein the expansion chamber isin fluid communication with the first cooling system.
 56. The cryogenicmedical system according to claim 55, wherein the coolant source is apressurized tank containing refrigerant therein.
 57. The cryogenicmedical system according to claim 55, wherein the first refrigerant isNO2 in gaseous phase, and the second refrigerant is NO2 in liquid phase.58. The cryogenic medical system according to claim 55, furthercomprising a fluid flow splitter in fluid communication with the coolantsource.
 59. The cryogenic medical system according to claim 55, furthercomprising a flow regulator disposed within the second cooling system.60. The cryogenic medical system according to claim 55, furthercomprising a scavenging system in fluid communication with the expansionchamber of the catheter.